The Exeter laboratory thyroid function test testing strategy uses TSH as a front-line test.
Secondary hypothyroidism due to pituitary disease will be difficult to detect using TSH as a front-line test, and cannot be expected to be picked up as a matter of routine given that such patients often have TSH values within the normal range resulting in apparent classification as “euthyroid”. The importance of clinical assessment, relevant diagnostic detail provided on request forms and verbal contact as necessary with the laboratory is essential to ensure the appropriate range of investigations, including other pituitary function tests, in each case.
Hypogonadism is almost always a feature of hypopituitarism and should be looked for when secondary hypothyroidism is suspected (by measurement of FSH and LH plus Testosterone in men or Oestradiol in women).
Summaries and a decision tree for undiagnosed patients are shown below.
FT4 reflexed only if TSH is abnormal
FOR SELECTED PATIENTS AND THOSE WITH A FULLY SUPPRESSED TSH (i.e. <0.03) AND NORMAL FREE T4
|SECOND LINE||FREE T3|